Molded plastic cable ties are known in the art and are used to secure a variety of elongated items such as wires, cables, hoses, tubes, in tight bundles. Specialized button head ties are also known in the art. A button head tie is essentially a plastic tie strap product constructed from two individual pieces, a flexible tie strap and a rigid button head. The strap is molded with a tail finger grip on one end and a wedge-shaped pawl, or wedge, on the other end that locks into the button head when both the wedge and the strap are passed through an aperture in the button head and then driven into the button head. Serrations extend along a portion of the length of the tie strap and are transversely defined within the tie strap between longitudinally-extending side rails, all features being duplicated on both sides of the tie strap. The button head may be round or any other shape with the aperture defined within the button head to accept the tie strap. The wedge also has teeth on it that are functionally adapted to engage with the serrations on the tie strap when the strap is looped back through the aperture of the button head. The button head aperture typically provides two-angled surfaces that substantially match the angles of the wedge. When the teeth of the wedge are engaged with the serrations of the tie strap and the bundle becomes tight, the wedge is driven downwardly into the head aperture thereby pinching and locking it against a portion of the tie strap. This type of button head tie is considered to be “bi-directional” because all the strap features are duplicated on both sides; thus allowing the strap to be inserted and fed through the aperture opening on either side of the wedge for engagement and bundling, which makes assembly faster and easier. Such button head ties serve to secure the resulting bundle to an adjacent structural member such as a vehicle frame rail, firewall, fender, body panel, bracket or the like. The strap encircles the items to be bundled and is secured by the wedge driving down into the button head and against the strap at the internal ramp of the button head. The button head, in turn, can extend into and bear against a hole that is formed in the structural member.
Button head ties are effective, convenient and easy to use. However, button head ties of current design and manufacture have several problems associated with their use. For example, it has been found that tie straps that are relatively thick and that have relatively narrow side rails are much more susceptible to bending shear stresses and tie strap breakage. It has also been found that tie straps that have serrations with relatively sharp corners, or peaks, tend to produce high stress concentrations along the tie strap, also making them much more susceptible to tie strap breakage. Also observed in previous button head tie strap designs is the fact that tie straps can be inadvertently inserted at an angle into the button head aperture. This is due to the internal geometry of the button head aperture side walls which forms excessive clearance for the strap width. During inadvertent angled strap insertion, proper engagement of the strap serrations with the wedge teeth is not possible which results in unexpected release of the bundle. Button head ties of previous designs and manufacture also limit the overall tensile strength of the loop formed by the tie strap. An example of this common type of button head tie is illustrated and claimed in U.S. Pat. No. 4,557,023 to Six et al. (the '023 patent). In the '023 patent, the button head includes a shelf or step (26) that functionally cooperates with a step surface (19) that is defined within each of the supporting edges (14) of the wedge (4). See FIGS. 1, 2, 4 and 5 of the '023 patent. Another example of a button head tie is illustrated and claimed in U.S. Pat. No. 5,386,615 to Bernard (the '615 patent). In the '615 patent, the button head similarly includes stops (44) that functionally cooperate to seat a locking head (20) of the strap (12). The wedge-shaped locking head (20) seated on stops (44) within the narrowing aperture (26) does not leave enough space for the strap (12) to be inserted back through without unseating the locking head (20). See FIG. 5 of the '615 patent. When the strap (12) is further tightened around a bundle, the locking head (20) is pulled back down and seated against the stops (44). See FIG. 6 of the '615 patent.
Subsequently, this inventor has realized that the entire surrounding geometry, for both the button head and wedge, required to create the “shelf,” “stop” or “step” configurations mentioned above enables the “unexpected release of the bundle” and, furthermore, limits the ultimate potential wedging action of the button head tie. If the wedging action is improved, higher forces will be encountered, thus requiring additional structural reinforcement within the button head. Also observed in previous designs is the difficulty of inserting the strap into the button head when the button head aperture is concealing the wedge because the button head is free to slide in the region of the wedge, thereby sometimes blocking the open passageway the strap is intended to pass through.
In the view of this inventor, extensive improvements to the button head tie of the prior art are needed.